It is known to implement beam shaping based on the alignment orientation of liquid crystal molecules in a liquid crystal cell. This alignment can be controlled by applying an electric field thereto. The reorientation of the liquid crystal molecules results in a refractive index gradient, which leads to a light ray passing through the liquid crystal cell being redirected. Thereby, the direction and/or shape of a light beam can be controlled electrically.
Autostereoscopic display devices include a display panel having an array of display pixels for producing a display and an imaging arrangement for directing different views to different spatial positions in front of the display. It is well known to use an array of elongate lenticular elements which are provided extending parallel to one another and overlying the display pixel array as the imaging arrangement, and the display pixels are observed through these lenticular elements. Such displays are examples of multiview displays.
In an arrangement in which, for example, each lenticule is associated with two columns of display pixels, the display pixels in each column provide a vertical slice of a respective two dimensional sub-image. The lenticular sheet directs these two slices and corresponding slices from the display pixel columns associated with the other lenticules, to the left and right eyes of a user positioned in front of the sheet, so that the user observes a single stereoscopic image. The sheet of lenticular elements thus provides a light output directing function.
In other arrangements, each lenticule is associated with a group of four or more adjacent display pixels in the row direction. Corresponding columns of display pixels in each group are arranged appropriately to provide a vertical slice from a respective two dimensional sub-image. As a user's head is moved from left to right, a series of successive, different, stereoscopic views are perceived creating, for example, a look-around impression.
The above described device provides an effective three dimensional display. However, it will be appreciated that, in order to provide stereoscopic views, there is a necessary sacrifice in the horizontal resolution of the device. This sacrifice in resolution is unacceptable for certain applications, such as the display of small text characters for viewing from short distances. For this reason, it has been proposed to provide a display device that is switchable between a two-dimensional mode (singleview mode) and a three-dimensional (stereoscopic) mode (multiview mode).
One way to implement this is to provide an electrically switchable lenticular array. In the two-dimensional mode, the lenticular elements of the switchable device operate in a “pass through” mode, i.e. they act in the same way as would a planar sheet of optically transparent material. The resulting display has a high resolution, equal to the native resolution of the display panel, which is suitable for the display of small text characters from short viewing distances. The two-dimensional display mode cannot, of course, provide a stereoscopic image.
In the three-dimensional mode, the lenticular elements of the switchable device provide a light output directing function, as described above. The resulting display is capable of providing stereoscopic images, but has the inevitable resolution loss mentioned above.
In order to provide switchable display modes, the lenticular elements of the switchable device can be formed as a beam shaping arrangement of an electro-optic material, such as a liquid crystal material, having a refractive index that is switchable between two values. The device is then switched between the modes by applying an appropriate electrical potential to planar electrodes provided above and below the lenticular elements. The electrical potential alters the refractive index of the lenticular elements in relation to that of an adjacent optically transparent layer.
A more detailed description of the structure and operation of the switchable device can be found in U.S. Pat. No. 6,069,650.
WO 2008/126049 discloses a beam shaping device which uses first and second in-plane electrodes, which generate an in-plane electric field. This is found to enable a larger refractive index gradient, and thereby a more efficient beam divergence/convergence can be achieved. In preferred arrangements, the beam shaping device has a set of electrodes, driven to different potentials, to define a smooth change in refractive index across the shape of the beam shaping device. This document also discloses the use of additional thick layers to increase the focal distance by influencing the electric field that is generated within the LC layer.
This approach forms lenticulars based on so-called gradient-index (GRIN) lenses. These switchable lenticulars are based on a liquid-crystal (LC) layer sandwiched in between a flat substrate and a flat cover layer. The substrate is equipped with a rather complicated structure of electrodes. By putting the correct distribution of potentials on these electrodes, lenses are obtained with good optical quality. Compared to replica-based switchable lenticulars, GRIN-based switchable lenticulars have several advantages:
Their manufacturing is compatible with LC-panel fabrication technology in existing LC-panel factories and they have a perfect 2D-mode.
This invention aims to reduce the complexity of the structure implementing GRIN lenses.